A cigarette packing machine comprises a number of packing conveyors, each of which has a number of pockets spaced along an endless path and for receiving and conveying respective groups of cigarettes; and the packing conveyors are connected to feed devices for feeding packing materials to the packing conveyor pockets.
Cigarette packing machines are normally “intermittent” machines, i.e. the packing conveyors are operated intermittently (or “in steps), whereby a stop phase, during which the pockets are stationary, is alternated cyclically with a go phase, during which the pockets advance a given distance. In an “intermittent” packing machine, the groups of cigarettes are transferred between two successive packing conveyors at the stop phase.
The output rate of “intermittent” cigarette packing machines has increased continually to a present rate of close to 700 packets a minute, which has been achieved by gradually reducing the duration of the stop phase and increasing the average speed of the go phase. So doing, however, has inevitably increased the acceleration to which the groups of cigarettes are subjected, and has made it necessary to redesign all the component parts of the packing machines to reduce mechanical stress of the groups of cigarettes. This has called for the adoption of sophisticated, highly precise mechanical solutions, which inevitably increase the overall cost of the packing machines, so that modern packing machines are extremely fast, but also extremely expensive to produce and maintain.
To increase the output rate of a cigarette packing machine without increasing the acceleration to which the groups of cigarettes are subjected, a “twin-line” cigarette packing machine has been proposed, i.e. comprising two parallel packing lines. The end result, however, has been no more than a modest increase in output alongside a considerable increase in production cost. In a “twin-line” packing machine, in fact, a problem on one line results in stoppage of the entire machine, i.e. both lines, with obvious repercussions in terms of average output.
To increase the output rate of a cigarette packing machine without increasing the acceleration to which the groups of cigarettes are subjected, a “continuous” cigarette packing machine has also been proposed, whereby the packing conveyor pockets are advanced at constant speed, and the groups of cigarettes are therefore transferred between two successive packing conveyors while the packing conveyors are moving. Though fairly satisfactory in terms of output and the quality of the packets of cigarettes produced, “continuous” cigarette packing machines are mechanically complex and therefore expensive to produce and difficult to set up.